Microwave hollow guide power divider



1953 J. F. ZALESKI 2,649,575

MICROWAVE HOLLOW GUIDE POWER DIVIDER Filed Oct. 20, 1951 WWW i l! iiiimis ,5 IWHUHIM E INVENTOR. Joy/v A ZALJ/V/ Patented Aug. 18, 1953 .MICROWAVE HOLLOW GUIDE POWER DIVIDER John F. Zaleski, Valhalla, N. Y., assignor to General Precision Laboratory Incorporated, a

corporation of New York Application October 20, 1951, Serial No. 252,356

8 Claims.

This invention pertains to microwave power dividers and more specifically to such devices for use in connection with rectangular guides.

In variable power dividers for microwave energy it is highly desirable to have continuous, smooth control of the division of power between the input and two or more output terminations. One of the major difiiculties in such devices is in providing substantially constant impedance to the input termination or generator for all positions of adjustment. Also, it is desired that the discrimination factor between maximum and minimum positions be relatively high, such as not less than 20 db.

In prior devices where reasonably constant impedance is obtained other difiiculties have been encountered. In some or the simpler types of variable power dividers it has been the practice to provide septums, vanes, posts or resonant rings internally oi the junctions. pacitance joints through which these internally moving parts must be operated give rise to R-F leakage and at the same time these internal parts alter the voltage gradients in the junctions and lower the breakdown voltage. Since wave guides are often operated at near maximum capacity it is highly desirable that microwave power dividers have a voltage breakdown as high as a straight piece of wave guide.

It is the primary object of the present invention to provide an improved, simple microwave power divider which minimizes the prior difficulties while at the same time having improved characteristics.

Another object is to provide an improved hol low guide power divider having such angles among the three arms that any arm can be employed as the input arm, with the remaining two constituting the output arms.

Still another object is to provide an improved hollow guide power divider in T form, the output arms being coaxial.

The device of the invention consists basically of three or more microwave rectangular guides meeting in an H-plane junction, all of their broad faces being parallel. At the junction of the several rectangular guides a microwave short-circuited hollow wave guide stub is placed so that its axis is perpendicular to the plane of the axes of all of the guides. This stub has a length substantially equal to an odd integral multiple of one-quarter of the wavelength in the guide and is rotatable. It therefore, in combination with the junction impedance, imposes an open-circuit condition upon any guide arm The necessary caacross which it is positioned, and on the other hand the stub does not affect the impedance of a guide arm when positioned longitudinally thereto. As the stub is rotated, it accordingly completely interdicts each of the two output arms in turn as it is turned approximately crosswise thereto, and partly interdicts each arm. as the stub is turned to intermediate positions.

,A further understanding of the invention may be secured from the detailed description and the associated drawings, in which:

Fig. 1 represents a plan view of one embodiment of the power divider.

Fig. 1a is a partial cross section on line ia-Ia of Fig. 1.

Fig. 2 is a cross sectional elevational view of Fig. 1 on the line 2--2.

Fig. 3 represents a plan view of an embodiment having 180 separation of the output arms.

Referring now to Fig. l, a rectangular hollow guide II is joined at equal angles to two other similar guides 12 and I3. The angle A between guides I 2 and i3 is 90. In the drawing the junction and guides are shown in plan, with a broad face of each of the guides presented. The guide cross section is rectangular as shown in Fig. 1a. The cross sections of the arms 12 and H are similar. The axes of all of the arms are in the same plane and accordingly the broad sides 16, H, and ll) of all three guide arms are in the same plane. Such a junction of microwave guides is known as an H-plane junction, and in a manner well understood in the art its impedance discontinuity may be made zero by the use of suitable matching means such as irises, tuning screws or posts. For example, if the arm ll be supplied with microwave energy of a frequency suitablefor the size wave guide employed, and if suitable irises I9 and 2| be put in the two arms l2 and I3, the supplied energy will be divided equally to flow out of the two arms 12 and I3, provided of course, that the latter arms are terminated in their characteristic impedances, and no impedance discontinuity will be observed at the input arm I I.

At or near the point at which the three longitudinal axes of the three arms meet, a, rectangular guide stub 22 is erected with its longitudinal annular collar 23 which rotatably engages an annular recess at 24 in the common top face of the junction of the three arms, here represented at I6 and I8. The collar 23 is provided with a cylindrical groove 26 that is of such dimensions as to constitute a quarter-wave choke to prevent the leakage of any microwave energy through the rotatable mechanical joint. The internal length L of the stub 22 is approximately an odd integral multiple of one-quarter wavelength in the guide. The broadband characteristic of the power divider is influenced by the magnitude of this odd integral multiple. If it is unity, the device has the widest possible frequency response, while if this odd multiple is greater than unity, the frequency response becomes correspondingly narrower.

Referring again to Fig. 1, the major transverse axis of the adjustable guide stub 22 is shown at an angle B of approximately 22 degrees from the extended center line of the input guide arm II, which angle is one-half of the angle that the arms I2 and I3 make with this line. This angle B is that at which the transmission from the arm I I into the arm I2 is maximum. At the same angle the transmission from the arm II into the arm I3 is very slight, tests showing the energy emitted from the interdicted arm I3 to be more than db below that emitted from the arm l2. When the stub 22 i turned to an angle of 22 /2 on the opposite side of the extended center line of arm II, the arm I3 becomes the output arm and substantially no energy escapes from arm I2.

Summarizing, when the adjustable stub is turned to a position 22 from its center position, as illustrated, substantially all power put into arm II is delivered out of arm I2 with no power output at arm I 3, and When the stub is turned clockwise, substantially all power put into arm II is delivered out of arm I3 with no power at arm I2. In intermediate positions output power is divided between arms I2 and I3, varying approximately in accordance with the square of the cosine of the angle between the axis 25 of the stub 22 and the longitudinal axis of the arm I I.

In refinement of the design to secure complete absence of all reflection into the input arm the length L of the stub is preferably varied slightly from an exact odd quarter-wave multiple, in order to neutralize, by the reactance thereby introduced, the oppositely phased reactance caused by the departure of the construction from that of a simple Y junction with iris matching.

The described power divider has the same power handling capacity as a straight length of a simple rectangular guide, as there are no internal projections to shorten the electric field path.

In the embodiments shown, the quarter-wave stub rotates about an axis passing through the point of intersection of all of the arms. All such embodiments will operate in the reverse direction. In other words, if microwave energy is fed into the ends of the arms l2 and I3 toward their common junction energy from only one of the respective arms will enter the arm II when the stub is at either of its two terminal positions. If the two inputs are equal in magnitude and exactly alike in phase, when the stub is in the intermediate position the inputs will be added to form a constant output.

If the angle A be made 120, the three arms will be equally placed 120 apart, and if no matching means are employed, or if. match ng means are symmetrically placed, any arm can be employed as input and the remaining two as output arms with a relatively low standing wave ratio at all positions of the rotatable stub. In this case the angle B is approximately 30.

If the angle A is made 180 th T construction of Fig. 3 results, which has advantages of convenience in some cases. In Fig. 3, when the stub 22 is placed in the position shown by the solid lines, so that its major transverse axis 30 makes an angle of approximately 45 with the center line of the input arm 28, the output of the arm 29 is maximum and is almost exactly equal to the input energy. The output of the arm 3| is substantially zero. Rotation of the stub 22 by in a clockwise direction to the dashed position 32 transfers the output to the arm M. In intermediate positions the ratio of the outputs of the two arms is a function of the angle between the axis 30 and longitudinal axis of the arm 28. In the center position there is no excitation of the stub at all and the energy is equally divided in like phase between the two output arms 29 and 3I.

In rotating the quarter-wave stub 22 from its depicted solid-line terminal position to its dashed-line terminal position, if the junction is to present constant impedance to the input arm for all positions of stub 22, the rotation must be clockwise as seen in the drawing, so that in the mid position of the stub its transverse major axis parallels the longitudinal axis of the arm 28. Otherwise, the stub 22 would at one point of its rotation be transverse to the input arm, in which position the stub would present infinite impedance thereto, and no energy whatever would pass through the power divider.

In all embodiments of the invention, the quar ter-wave stub 22 may be rotated manually by a suitable knob 39 on the shaft 38 attached to the body of the stub. The relative angular position of the stub may be indicated by a pointer and index assembly 40.

In order to avoid the possibility of the stub 22 being moved to positions where its major transverse dimension would be perpendicular to the longitudinal axis of the input arm, in which event a great variation in impedance would be presented to the input arm, suitable stops 4| and 42 may be provided for limiting the rotational movement of the stub 22 over the optimum range mentioned above the range being centered on the axis of the input guide arm.

The lesser cross-sectional dimension of any rectangular guide may be reduced with no effects except those of decreasing the characteristic impedance and of reducing the breakdown voltage limit. Therefore, since the function of the quarter-wave stub in all of the embodiments of this invention is to reflect high impedance to the uide junction, the stub may often be made thinner than the standard dimension for rectangular guide without affecting its operation, and in some cases design considerations may indicate the desirability of such a reduction in thickness.

What is claimed is:

1. A microwave power divider comprising, a rectangular hollow guide arm, a pair of rectangular hollow guide arms meeting said arm in a junction, the broad faces on the same side of each of said three arms being in a common plane, a rectangular quarter-wave short-circuited stub rotatably attached to the broad faces of one side of said junction with the longitudinal axis'of said s b o al o aid common plane and coincident with the axis of said junction, and means for rotating said stub about its longitudinal axis.

2. A microwave power divider comprising, a rectangular hollow microwave guide input arm, a pair of rectangular hollow microwave guide output arms connected to said input arm at an H-plane junction and making equal angles with said input arm, one broad face on the same side of each of said input and output arms being in a common plane, matching means in selected ones of said arms for preventing reflection from said H-plane junction into said input arm, a rectanular hollow guide short-circuited stub having a length of approximately an odd integral multiple of one-quarter wavelength in guide rotatably attached to said junction with its longitudinal axis normal to said common plane at said H-plane junction, said common planar junctured faces of said arms containing at said H-plane junction an aperture afiording conductive microwave access between the interior space of said junction and the interior space of said stub, and means for adjustably rotating said stub about its longitudinal axis.

3. A microwave power divider in accordance with claim 2 in which said equal angles are each 120.

4. A microwave power divider in accordance with claim 2 in which said equal angles are each 90".

5. A microwave power divider in accordance with claim 2 in which said means for rotatably attaching said stub to said junction about its longitudinal axis comprises a collar surrounding said stub and provided with a wave trap slot.

6. A microwave power divider for rectangular hollow guide comprising, an input branch adapted for energization by microwave energy of a selected wavelength, a pair of output branches making H-plane equiangular junctions therewith, means in selected ones of said branches for neutralizing junction impedance discontinuities, a rectangular hollow guide short-circuited stub having a length of approximately an odd integral multiple of one-quarter wavelength in guide at the frequency of said microwave energy, said stub being rotatably attached to said junction with its longitudinal axis normal to said plane, means for rotating said stub about its longitudinal axis, and means for limiting rotation to a range including: one terminal position providing maximum discrimination between output branches through the intermediate position providing minimum discrimination between output branches to the other terminal position providing maximum discrimination in the reverse order.

7. A microwave power divider comprising a rectangular hollow microwave guide input arm, a pair of rectangular hollow microwave guide out put arms meeting said input arm in an H-plane junction, the broad face on the same side of each of said input and output arms being in a common plane, matching means in said arms for preventing reflection from said junction into said input arm, a quarter-wave short-circuited micror wave stub adjustably attached to said junction with its longitudinal axis normal to said common plane to be placed across either output arm and forming at the operating frequency a high resonant impedance.

8. A microwave power divider comprising a rectangular hollow microwave guide input arm, a pair of rectangular hollow microwave guide output arms meeting said input arm in an H-plane junction, the broad face on the same side of each of said input and output arms being in a common plane, matching means in said arms for preventing refiection from said junction into said input arm, a quarter-wave short-circuited microwave stub rotatably attached to said junction with its longitudinal axis normal to said common plane, said stub having a rectangular opening for passing the operating frequency of said arms, whereby said stub presents a resonant impedance to said output arms in accordance with the rotational position of said rectangular opening relative to the respective arms.

JOHN F. ZALESKI.

References Cited in the file of this patent published by McGraw-I-Iill, 1948, pages 537-539 relied on. (Copy in Div. 69.) 

